The 2009 ITRS update specifies wafer overlay control as one of the major tasks for the sub 40 nm
nodes. Wafer overlay is strongly dependent on mask image placement error (registration errors or
Reg errors)<sup>1</sup> in addition to CD control and defect control. The specs for registration or mask
placement accuracy are twice as difficult in some of the double patterning techniques (DPT). This
puts a heavy challenge on mask manufacturers (mask shops) to comply with advanced node
Registration test masks as well as production masks were measured on a standard registration tool
and the registration error was calculated and plotted. A specially developed algorithm was used to
compute a correction lateral strain field that would minimize the registration error. A laser based
prototype RegC<sup>TM</sup> tool was used to generate a strain field which corrected for the pre measured
registration errors. Finally the post registration error map was measured. The resulting residual
registration error field with and without scale and orthogonal errors removed was calculated.
In this paper we present first results of registration control experiments using the prototype
Currently all LMS IPRO pattern placement metrology tools are calibrated using a 1D length standard provided by a
national standards institute (e.g. NIST or PTB), however there are no 2-D standards available with an uncertainty
matching the requirements of mask manufacturing for the 22nm HP node and beyond. Therefore, the 2D stage
coordinate system of the LMS IPRO systems is calibrated using KLA Tencor's proprietary combined correction
With introduction of the LMS IPRO4 into high volume mask production at the AMTC, AMTC and KLA-Tencor MIE
have demonstrated the capability to match IPRO3 and IPRO4 grids within 1.2 nm uncertainty . Using the Golden Tool
approach, we achieved a significant improvement in pattern placement measurement capability of previous generation
measurement tools of up to 30%. This in turn leads to improved pattern placement metrology fleet capability and
extended useful lifetime of capital equipment.
The use of multiple high end registration measurement tools enables the creation of a 2D coordinate system standard,
which could be used for improved fleet matching and would help improve the capability of older generation pattern
placement metrology tools by matching to this standard. Within this paper Golden Tool and Round Robin worldwide
fleet matching approaches are compared and discussed.
The development of the 45-nm node manufacturing process at leading edge mask shops is nearly finished. In order
to reach the required registration measurement performance with a precision to tolerance value of P/T=0.25,
the measurement error may not exceed 1.2 nm according to ITRS roadmap. This requires the latest generation
of registration measurement tools. In addition, the demand for measuring very small features increases - for
standard pattern placement measurements, as well as special engineering tasks, e.g., the position measurement
of single contact holes.
In this work, the error of pattern placement measurement on an LMS IPRO4 is determined using an analysis
of variance methodology (ANOVA). In addition we analyze the capability as a function of the critical dimension
(CD) of the registration feature. The results are compared to the previous tool generation.
Following the international technology roadmap for semiconductors
the image placement precision for the 65nm technology node has to be 7nm. In order to be measurement capable, the measurement error of a 2D coordinate measurement system has to be close to 2nm. For those products, we are using the latest Vistec registration metrology tool, the LMS IPRO3. In this publication we focus on the tool performance analysis and compare different methodologies. Beside the well-established ones, we are demonstrating the statistical method of the analysis of variance (ANOVA) as a powerful tool to quantify different measurement error contributors. Here we deal with short-term, long-term, orientation-dependent and tool matching errors.
For comparison reasons we also present some results based on LMS IPRO2 and LMS IPRO1 measurements. Whereas the short-term repeatability and long-term reproducibility are more or less given by the tool set up and physical facts, the orientation dependant part is a result of a software correction algorithm.
We finally analyse that kind of residual tool systematics and test some improvement strategies.
In case drastic changes need to be made to tool configurations or blank specifications, it is important to know as early as possible under which conditions the tight image placement requirements of future lithography nodes can be achieved. Modeling, such as finite element simulations, can help predict the magnitude of structural and thermal effects before actual manufacturing issues occur, and basic experiments using current tools can readily be conducted to verify the predicted results or perform feasibility tests for future nodes. Using numerical simulations, experimental mask registration, and printing data, the effects on image placement of stressed layer patterning, pellicle attachment, blank dimensional and material tolerances, as well as charging during e-beam writing were investigated for current mask blank specifications. This provides an understanding of the areas that require more work for image placement error budgets to be met and to insure the viability of optical lithography for future nodes.
A NIST traceable phase1 shift standard has been designed, fabricated, and tested on three phase shift measurement tools using different wavelengths. By using the fundamentals of NIST traceable step height, quartz index, and the understanding of the illumination optics of the Lasertec phase metrology tool, a phase standard has been created which can be used to calibrate Lasertec phase metrology tools. The pattern that is used is compatible with the recommended best practices for calibrating and measuring step heights and phase on the Lasertec tools. The mask is made with multiple depths. The three mask depths allow for the mask to be calibrated to three NIST traceable depth heights. This was done using the FEI SNP XT depth metrology tool. Since the mask format is mask based (6x250 Cr on quartz), it can be easily used on mask manufacturing metrology systems. The depths are targeted at the 180-degree phase shift for 157nm, 193nm, and 248nm lithography. The mask can be used to set targets and check the linearity of the phase metrology tools. The patterns are compatible with AFM and Profilometer depth metrology tools as well as multiple Lasertec spot sizes and shearing distances. The quartz depths are fabricated using a wet quartz etch process. The wet etch minimizes the quartz roughness and removes that error source from the metrology. The pattern is also arrayed so that multiple sites can be used to confirm the metrology and the prime measurement site could be changed if there was a suspicion of pattern damage or contamination.
An assessment of the mechanical performance of pellicles from different vendors was performed. Pellicle-induced distortions were experimentally measured and numerical simulations were run to predict what improvements were desirable. The experiments included mask registration measurements before and after pellicle mounting for three of the major pellicle suppliers, and adhesive gasket material properties characterization for previously untested samples. The finite element numerical simulations were verified via comparison to experimental data for pellicles with known frame bows, measured by the vendor. The models were extended to simulate the effect of the chucking of reticles in an exposure tool, as well as the various magnification correction schemes available in such tools. Results were compared to ITRS requirements to evaluate performances. This study enables the AMTC to give important feedback to pellicle suppliers and make proper recommendations to customers for future pellicle choices.